1. Field of the Invention
The present invention relates to a semiconductor device having a current detection circuit and a method for manufacturing the semiconductor device.
2. Description of the Background Art
Recently, the field of automotive electronics has been rapidly developed due to the increase of social awareness of car safety, low fuel consumption and pollution reduction.
To detect a current value flowing into a system (device) such as an on-vehicle transmission, a current detection resistor (hereinafter referred to as shunt resistor) is disposed in the system. A voltage drop in the shunt resistor is measured to perform current-voltage conversion and obtain a voltage value (hereinafter referred to as detected voltage value) based on a current value to be detected. The detected voltage value is converted into a current value by arithmetic processing in a control circuit in the system.
It is desirable that the shunt resistor has low resistance in order to reduce power loss. It is therefore desirable that the shunt resistor is constituted by a resistor with a small sheet resistance value. A metal wire of Al—Si—Cu (aluminum-silicon-copper) or the like (hereinafter referred to as Al—Si—Cu metal wire), a diffused resistor in which high concentration impurities have been implanted, a polysilicon (poly-Si) resistor, etc. may be used as the shunt resistor.
The resistance value of the shunt resistor may vary due to manufacturing factors etc. When the resistance value of the shunt resistor varies, a desired detected voltage value cannot be obtained but an error is caused in detection of the current value. When the error in detection of the current value affects operation of the system, trimming (adjustment) should be performed on the shunt resistor. Next, a method for trimming the shunt resistor will be described. FIG. 17 is a circuit diagram showing the circuit configuration of a current detection circuit according to the background art.
In the current detection circuit shown in FIG. 17, an MOSFET (Metal Oxide Semiconductor Field Effect Transistor) 62 is used as an MOS type shunt resistor and trimming is performed by use of change of an ON resistance of the MOSFET 62 caused by a gate voltage. This current detection circuit has been disclosed, for example, in JP-A-2005-234781 (FIG. 1). In FIG. 17, the reference sign 52 denotes a current control element; 53, a load resistor; 54, a current mirror circuit; 54a and 54b, pnp transistors; 55a and 55b, constant current sources; 56, an operational amplifier; 61, a constant current control circuit device; 62, a p channel MOSFET (resistance control element); 63, an emitter resistor; 64, a CrSi (chrome silicon) resistor; and 65, a temperature characteristic correction circuit.
In addition, another trimming method will be described. FIG. 18 is a plan view showing a main part of the configuration of a trimming resistor element 80 according to the background art. The trimming resistor element 80 shown in FIG. 18 is provided with a plurality of double resistance region type trimming resistors 71-1 to 71-9 each partially having a high resistance region RH and a single resistance type trimming resistor 71-10 entirely having a high resistance region RH. This trimming resistor element 80 is formed in the system in advance. Metal wires 74-1 and 74-2 connecting these trimming resistors 71-1 to 71-10 are cut off by a laser to perform trimming. Such a trimming method has been disclosed, for example, in JP-A-2011-40497 (FIG. 8).
JP-UM-A-62-193571 discloses a large current measurement device which applies a current to a resistor line, measures a voltage generated in the resistor line, converts the measured voltage into a current value and displays the current value, wherein: a variable resistor (not lower than twice as high as a resistance value of 100Ω) is connected between opposite ends of the resistor line and adjusted to make a voltage value between opposite ends of the variable resistor equal to a predetermined voltage value when a specific current is applied to the resistor line.
In addition, JP-A-4-137559 and JP-A-2012-85163 disclose a semiconductor integrated circuit in which a variable resistor is constituted by a circuit formed by connecting a plurality of resistors in series and a selection circuit.
In addition, JP-A-2006-136086 (FIG. 2) disclose a method in which a source-drain voltage of an MOSFET is divided by two resistive elements with different temperature coefficients so that change of a detected voltage caused by an operating temperature can be corrected and a source-drain current flowing into the MOSFET can be obtained with high accuracy.
However, in the method in which the MOSFET 62 is used as a shunt resistor as in the aforementioned FIG. 17 or the aforementioned JP-A-2005-234781 (FIG. 1), it is necessary to apply analog control to the gate voltage by means of the operational amplifier etc. in order to correct a variation of the resistance value of the shunt resistor. The circuit for controlling the gate voltage becomes complicated as illustrated.
In addition, in the method in which the trimming resistor element 80 is used as a shunt resistor and the shunt resistor is directly trimmed as in the aforementioned FIG. 18 or the aforementioned JP-A-2011-40497 (FIG. 8), the circuit can be simplified but an expensive device such as a laser cutting device is required for the trimming.
In the aforementioned JP-A-2006-136086 (FIG. 2), an error in detection of the current value is caused when the ON resistance of the MOSFET or the resistance value of the voltage division resistor changes due to some process variation etc.
In addition, in response to a request to miniaturize the system, it is desired that the low-resistance shunt resistor can be obtained in a small area when the shunt resistor is disposed on the same chip as the integrated circuit (IC) including the control circuit.